A new look on the Jurassic formations of the western part of Iraq
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ORIGINAL PAPER
A new look on the Jurassic formations of the western part of Iraq Salim Q. Al-Naqib & Ali I. Al-Juboury
Received: 29 April 2012 / Accepted: 21 December 2012 # Saudi Society for Geosciences 2013
Abstract The Jurassic succession of western Iraq includes the Ubaid, Hussainiyat, Amij, Muhaiwir, and Najmah formations. Each formation is composed of basal clastic unit overlain by upper carbonate unit. Extensive and huge erosional unconformity occurred at the Triassic–Jurassic boundary due to marked shifting of structural (E–W) strike of the Triassic (Rhaetic) Zor Hauran Formation to (NE–SW) Jurassic formations. Sea level falling (lowstand system tracts) would result in the progradation of the land on the expense of the sea forming the recognizable progradation of the fluvial and deltaic deposits of the lower clastic units of the Jurassic formations, whereas sea level rising (highstand system tract), i.e., sea prograding, causes deposition of the carbonate units of the Jurassic formations system. This progradation resulted to various carbonate environments of deposition ranging from subtidal, intertidal, to supratidal. The main target on most of the exploration blocks in the western part of Iraq focused on the lower Paleozoic successions, whereas prospects in Triassic, Jurassic, and lower Cretaceous targets are less extensive but may have significant potential on certain blocks in both stratigraphic and structural traps. The western part of Iraq was subjected to intermittent pulses of uplifting (sea regression) and subsidence (sea transgression) to form the Jurassic basin system in the area. The Jurassic formations lack the characteristics of petroleum systems. In contrast, in the central and northern parts of Iraq, the Jurassic formations
S. Q. Al-Naqib Research Center for Dams and Water Resources, Mosul University, Mosul, Iraq e-mail: [email protected] A. I. Al-Juboury (*) Geology Department, Mosul University, Mosul, Iraq e-mail: [email protected]
(Najmah and Gotnia formations) were deposited in subsiding basins in which the reservoir and sealed evaporitic rocks existed. In turn, in the western desert of Iraq, the Jurassic formations lack these petroleum system characteristics. Hence, it can be proposed that the petroleum–nonpetroleum inflection could be proposed in the east of area km 160. Keywords Jurassic succession . Western desert of Iraq . Progradation . Deposition . Petroleum systems
Introduction Because of the geological and economical importance of the Jurassic successions in the western desert of Iraq, they have been described in numerous geological projects mainly by the Directorate General of Geological Survey and Mineral Investigation (formerly the State Organization for Minerals) and several books and reports (e.g., van Bellen et al. 1959; Buday 1980; Buday and Hak 1980; Karim and Ctyroky 1981; Al-Mubarak 1983; Jassim et al. 1984; Al-Naqib et al. 1985, 1986; Qasir et al. 1992; Jassim and Buday 2006) in addition to many academic theses and research papers, the majority of which
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